Scroll type fluid displacement machines such as scroll compressors have an orbital scroll that is driven in a generally circular orbit by a crankshaft. The crankshaft drives the orbital scroll at high speed and applies force to the orbital scroll that tends to force wraps on the orbital scroll into contact with the wraps of a fixed scroll. The crankshaft should not exert force on the orbital scroll in a direction parallel to the axis of rotation of the crankshaft.
The crankshaft in a scroll compressor drives a balance system as well as an orbital scroll. The balance system includes a scroll balancer and a crank-shaft balancer, and may also include balancing for other compressor functions and components. A balancer for the input drive may also be supported by the crankshaft.
A scroll compressor crankshaft must be accurately manufactured to drive an orbital scroll and to drive a balance system. It has been found that even small errors in machining a scroll crankshaft can result in substantial decreases in the useful life of a scroll compressor. The decrease in the useful life is primarily due to bearing misalignment. Conventional single crank crankshaft manufacturing and machining procedures have been unsatisfactory due to dimensional variations and tooling costs. Single crank crankshaft manufacturing procedures have included machining the main shaft and the web while the forging is mounted on centers. The single crank crankshaft is then removed from the centers, rechucked with a special eccentric or offset fixture which allows access to the drive stud and then the drive stud is ground. Offset fixtures are relatively expensive to make and require maintenance. This rechucking increases manufacturing deviations and increases cost. The increased manufacturing tolerance deviations increases the portion of crankshafts that are unacceptable.